Recomposite ceramic armor with metallic support strip

ABSTRACT

Carbon steel, alloy steels, titanium strips, directly under the joints and free edges of the ceramic face plates of ceramic composite armor improves performance of the armor; metal strips should be 0.5 to 1.5 inches in width, from 0.010 inches to 0.125 inches in thickness, and have a modulus of elasticity of at least 5 million p.s.i.

United States Patent Alliegro et a]. [45] Aug. 15, 1972 RECOMPOSITECERAMIC ARMOR [56] References Cited 2 WITH METAhLLIC SUPPORT STRIP UNTEDSTATES PATENTS 7 I t Ri d A.- ll 1 g f g' f g' g fgaggfig 3,509,8335/1970 Cook ..l09/82 Learned, 88 Dorset Rd., Holliston, Mass 01746Primary ExanunerStephen C, Bentley Attorney-Rufus M. Franklin [22]Filed: May 12, 1967 211 Appl. No.: 638,009 1 ABSTRACT Carbon steel,alloy steels, titanium strips, directly 52 us. Cl ..l09/83,' 161/404under the joints and free edges of the ceramic face 51 Int. Cl. ..F41h5/04, F4lh 5/26 Plates of ceramic Composite armor improves p 53 Fi ld fS h g9 3 3 199 79 0 1 formance of the armor; metal strips should be 0.5to

1.5 inches in width, from 0.010 inches to 0.125 inches in thickness, andhave a modulus of elasticity of least 5 million p.s.i.

6 Claims, 2 Drawing Figures PATENTEDAUBISIHYZ 3,683,828

NVENTORS- RICHARD A ALLIEGRO ADD/SON WLEARNED zzz ATTORNEY RECOMPOSITECERAMIC ARMOR WITH METALLIC SUPPORT STRIP BACKGROUND OF THE INVENTIONRecently light weight composite armor for protection against small armsfire has been developed by employing hard brittle ceramic facingmaterial to the back of which is bonded a glass fiber laminate of wovenglass cloth and consisting of several laminations held together by aresinous bond. When ceramic armor is hit, its high strength andhardness, and in particular its high modulus of elasticity, come intoplay in starting to defeat the projectile. Extremely high loading ratesare applied to both the projectile and the ceramic. When the stiffnessof the ceramic is sufficient to overload the projectile beyond its yieldpoint causing it to fracture, before the ceramic itself yields fully,the projectile will be stopped. Ifthe ceramic yields first, theprojectile will not be damaged sufficiently to initiate the orderlyexpansion of the load area to the backup and a penetration will occur.This expanded high load area is absorbed through an orderly delaminationof the backup material, generally a resin-starved fiberglasslaminant offrom to 24 layers.

This idealized system exists in a given area within an armor panel, thatis, a percentage of the total area will offer optimum protection. Asedges, corners, and boundaries of abutting plates are approached,ballistic performance will degrade. In the case of a 6 inch X 6 inchtile, roughly 60 percent will be substandard, a 12 inch X 12 inch tile,roughly 30 percent, and a inch X 15 inch, roughly percent. Thetechnology of going to large shapes has been realized, but the need for100 percent optimum protection is a real one and has not been attained.

Presently, raised edges are put on one ceramic system to strengthen thesusceptable area and thus improve its performance. This is a partialsolution; problems exist in making a reliable raised edge plate at a lowrejection level, limiting economic gains. Also there is a practicallimit to the differential between raised edge and center tile thickness,contributing to the center sections being over-designed, thus adding tothe systems weight. Keeping weight to a minimum is required sinceceramic armor systems are used to protect personnel (which means wearingthe armor) and helicopters, craft which are supersensitive to weightadditions. Weight costs in both areas have been expressed in terms offrom $50 to $300 a pound, lending impetus to the quest for the lightestarmor possible.

DESCRIPTION OF THE INVENTION Ceramic composite armor systems can beimproved at the joints and edges by adding a thin ribbon of metalbetween the ceramic and the fiber backing as shown in the drawings inwhich:

FIG. 1 shows a cross-sectional view of a joint in an armor system; and

FIG. 2 shows a cross-sectional view of reinforced edges in an armorsystem.

In FIGS. 1, l1 and 12 are adjacent ceramic tiles which form the facingof the armor, 13 is a metal strip extending along the full length ofjoint 14, and 15 is the glass fiber laminate backing material bonded tothe facing 11 and l2.

In FIG. 2, 16 is the ceramic facing plate, 17 and 18 are metal stripsextending along the full length of the 20 and 21 of the plate 16, and 19is the fiber laminate backing bonded to the plate 16.

The facing ceramic plates may be monolithic shapes of alumina, siliconcarbide, or boron carbide, The facing may be flat or curved dependingupon the particular employment of the armor. The following is an exampleof a flat armor made up of a plurality of adjacent boron carbide tiles,in which the improvement of the present invention is provided at boththe joints between the tiles and at the free edges of the whole plate.The invention may be applied to other shapes and systems, such as singlepiece breast plates in which the metal strip is provided along all thefree edges, or systems in which the ceramic facing is monolithicpolycrystalline alumina, or monolithic polycrystalline silicon carbide.

EXAMPLE Two 12 inch by 12 inch square flat tiles of polycrystallinemonolithic boron carbide, 0.340 inches thick, are butted together alongone edge. A steel strip 1 inch wide by 1 foot long is bonded to thetiles along the joint by a polysulfide resin or other suitable adhesivesuch as a polyurethane. The steel is oil hardening ground flat stock,SAE Type 01 (Marshall OILcrat), 0.030 inches in thickness. Additionalstrips of the same steel are bonded along the outer edges of the twoplates. A woven glass fiber backing consisting of 12 layers of wovenroving glass fiber bonded with 25 percent by weight of polyester resinbond (54 inch thick laminate, made from 23 ounce per yard, 1,000 poundper inch of width tensile strength warp yarn, and 800 pound per inch ofwidth tensile strength filling yarn; tensile strength of laminate being45,000 to 50,000 pounds per square inch; interlaminar shear strength oflaminate being 1,000 to 1,300 pounds per square inch) is bonded to theside of the ceramic plates to which the steel strips are attached by apolysulfide resin (Pro-Seal 8908, sold by Coast Pro-Seal & Mfg. Co., LosAngeles, California. The assembly is clamped and cured for 3 dayswithout heat or for 4 hours at 220 F. Other nonbrittle adhesives can beused such as commercially available polyurethanes.

The completed composite armor plate, upon subjection to ballistic testsshows no substantial reduction of protective action at the joints or atthe edges, as compared to the protection offered by the central portionsaway from joints and edges.

Although we have illustrated a carbon steel as a reinforcing material inthe example, alloy steels and titanium may be used. The support stripmust be metallic in nature and must have a modulus of elasticity of atleast l5 10 p.s.i. Because of the lower mass per unit volume fortitanium as compared to steels, the thickness of the strip, whentitanium is used should be roughly 1.5 times the thickness of anequivalent steel strip. Whatever metal is used a thickness of 0.125inches should not be exceeded, and a minimum thickness of 0.010 inchesis required for significant improvement. A thickness of 0.01 5 inches to0.060 inches is preferred and a width, at the joints of from 1 to 1.5inches is found most useful. At the free edges the width may be reducedto 0.5 inches, producing an overlap of 0.5 inches as in the case ofjoint protection when a 1 inch strip is used.

What is claimed is: 1. In a composite armor having a ceramic facing anda bonded laminate fibrous backing, the improvement consisting of: ametal strip, at least 0.5 inches wide and at least 0.010 inches thickalong the outer edges of the armor between the facing and the backing,said metal having a modulus of elasticity of atleast 15 X pounds persquare inch.

2. In a composite armor having a ceramic facing and a bonded laminatefibrous backing in which the ceramic facing is made up of at least twoplates butted together to form a joint, the improvement consisting of ametal strip at least one inch wide, along the joint, positioned betweenthe facing and the backing, said metal strip having a thickness between0.010 and 0.125

inches and a modulus of elasticity of at least X 10 pounds per squareinch.

3. The armor of claim 1 in which the metal is selected from alloysteels, carbon steels, and titanium.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 3 3828'Dated August 15, 1972 Inventor(s) I Richard A, ALLIEGRO and Addison W.LEARNED III It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

The title of the patent should read: COMPOSITE CERAMIC ARMOR WITHMETALLIC SUPPORT STRIP The assignment to NORTON COMPANY dated May 9,1967 and recorded June 16, 1972 on Reel 2865, Frame 216.

Signed and sealed this 6th day of February 1973.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.FLETCHER,JR.

Commissioner of Patents Attesting Officer FORM Po-1050 [10-69) USCOMMDC603764,

n U S. GOVUGNMENI PRINTING OHIC! I969 0* 366-H4

2. In a composite armor having a ceramic facing and a bonded laminatefibrous backing in which the ceramic facing is made up of at least twoplates butted together to form a joint, the improvement consisting of ametal strip at least one inch wide, along the joint, positioned betweenthe facing and the backing, said metal strip having a thickness between0.010 and 0.125 inches and a modulus of elasticity of at least 15 X 106pounds per square inch.
 3. The armor of claim 1 in which the metal isselected from alloy steels, carbon steels, and titanium.
 4. The armor ofclaim 2 in which the metal is selected from the group consisting ofalloy steels, carbon steels, and titanium.
 5. The armor of claim 4 inwhich the facing plate is selected from the group consisting of boroncarbide, alumina, and silicon carbide.
 6. The armor of claim 5 in whichthe metal is a carbon steel having a modulus of elasticity of 15 X 106pounds per square inch and a thickness of 0.030 inches.